The present invention relates to a marking method and an apparatus thereof, and particularly, to a laser marking method and an apparatus thereof in which marks such as numbers, symbols, or the like can be marked on products with high efficiency and precision by stamping in a semiconductor manufacture step.
Recent down-sizing of works such as semiconductor products and the like has accompanied demands for very small and precise marks to be recorded thereon. These demands have been almost satisfied by a laser marking apparatus. As an example of a conventional laser marking apparatus, Japanese Patent Laid-Open Publication No. 2-187287 discloses a method in which a mask surface is subjected to raster-scanning by deflecting a laser beam from a laser oscillator and the laser beam having passed through the mask effects marking on a surface of a work. In this case, a mark equivalent to a stamp mark is divided and displayed on a liquid crystal mask. A laser beam is made pass through the liquid crystal mask by raster-scanning, and is thereafter irradiated on the surface of a work by a deflector thereby effecting scanning for stamping. This operation is repeatedly performed on successive divisional patterns, thereby to achieve stamping of the entire patterns.
However, the laser marking apparatus described above needs two deflectors, i.e., one for deflecting the laser beam injected onto a pattern displayed on the mask thereby to perform raster scanning and another for deflecting the laser beam transmitted through the mask in a direction toward a work transport line and for performing scanning in the X- and Y-directions on the surface of the work to synthesize the patterns. As a result of this, an X-Y deflection scanning drive system is required for a laser beam injection path and for a mask transmission light path, resulting in a drawback that large equipment must be used and a number of objects must be controlled.
In order to overcome the drawback described above, for example, developments have been made to a laser marking method and an apparatus thereof which is particularly advantageous for a system of marking a stamp mark displayed and divided into patterns on a mask and which improves the stamping precision while facilitating the stamping operation depending on divisional synthesis, as disclosed in Japanese Patent Laid-Open Publication No. 6-226476.
The laser marking method disclosed in this publication has a basic structure adopting a system in which a mask capable of displaying a marking pattern is scanned with a laser beam from a laser oscillator by a first deflector, thereby selectively transmitting the laser beam, and the laser beam transmitted through the mask is thereafter deflected by a second deflector so as to irradiate a work surface for marking. Divisional patterns, each corresponding to one scanning line of the first deflector, are sequentially displayed on the mask, and the deflection position of the beam on the work surface by the second deflector is shifted by an amount equivalent to one scanning operation in a direction perpendicular to the scanning direction for every transmitted scanning beam deflected by the first deflector with respect to a divisional patterns so as to synthesize and stamp the pattern.
According to the structure as described above, a stamp pattern divided corresponding to a scanning line in one direction by the first deflector are sequentially displayed on the mask in divisional patterns as units, and the laser beam is emitted for scanning along the display line for every divisional pattern. Specifically, the first deflector needs only to perform scanning in one direction and can therefore be constructed by only a polygon mirror, for example. In addition, the scanning beam to be transmitted through the mask is shifted by one divisional pitch to perform the next scanning operation upon completion of scanning one divisional pattern with use of the second deflector. Thus, the beam entering into the mask is deflected so as to scan the X-direction and the beam output through the mask is deflected so as to scan the Y-direction, so that divisional patterns of the mask are thereby synthesized and stamped. Therefore, an irradiation of the laser beam onto a mask needs not be subjected to raster scanning and factors to be controlled can be reduced in comparison with prior art. As a result, the design of the control system is simplified and the controlability is remarkably improved without lowering the manufacturing efficiency.
Meanwhile, as will be widely known, a laser beam has such an energy distribution which is maximum at an optical axis portion, gradually decreases toward the periphery, and spreads like a skirt in the vicinity of the outer circumference, to be close to zero, i.e., a so-called Gaussian distribution. Therefore, a processed mark has a half-circular shape which is deep in the center portion and is shallow toward the periphery if stamp processing is carried out with a laser beam irradiated onto one point.
Even in consideration of such an energy characteristic of the laser beam, the laser marking method disclosed in Japanese Patent Laid-Open Publication No. 6-226476 described above is capable of controlling the energy distribution to be substantially uniform in the scanning direction and achieved stamping with high precision, by superposing a part of an irradiation region of each of irradiation points adjacent to each other on work in the scanning direction of the laser beam. Further, this control is easily realized by relatively selecting the most efficient values for the scanning speed of the laser beam and the pulse distance of the points of irradiation.
According to this marking method, as described above, a shift by one divisional pitch is carried out in a direction perpendicular to the scanning direction to perform next scanning upon completion of scanning with use of the beam transmitted through the mask with respect to one divisional pattern. Therefore, divisional patterns adjacent to each other on the work are sequentially stamped, one after another, such that one of the divisional patterns is stamped by every one scanning operation. The energy distribution of the laser beam in the divisional direction also suggests a Gaussian distribution as described above for every divisional pattern, as shown in FIGS. 2(b) and 2(c). Consequently, a processed stamp is shallow at an end portion of each divisional pattern in the direction perpendicular to the scanning direction of the laser beam, on the surface of the work 10, as shown in FIG. 2(a), and the depth of the processed stamp increases toward the center portion, thereby forming a shape having a substantially half-circular cross-section. As a result of this, as shown in FIG. 19, small linear shades parallel to each other appear over the entire mark when viewing the surface of the work 10, and the stamping precision is thus not satisfactory.
In order to avoid generation of such shades, a part of each of adjacent laser beams should be superposed in the division direction like in the scanning direction. The simplest method will be a method of performing scanning with the distance between adjacent laser beams reduced in the division direction. Specifically, scanning is performed while superposing a part of each of spot irradiation of laser beams in the division direction with respect to one divisional pattern. This operation, however, is not suitable for use because the marking process period is inevitably elongated and the manufacturing yield is very lowered.